She was Nicolas Sarkozy's pin-up for diversity, the first Muslim woman with north African parents to hold a major French government post. But Rachida Dati has now turned on her own party elite with such ferocity that some have suggested she should be expelled from the president's ruling party.

Dati launched a blistering attack on the prime minister, François Fillon, under whom she served as justice minister, accusing him of sexism, elitism, arrogance and hindering the political advancement of ethnic minorities.

The row started over who will run for parliament in a wealthy rightwing constituency on the left bank in Paris, a safe seat for Sarkozy's ruling UMP. Dati is already a local mayor in the neighbourhood, a job felt to have been handed to her on a plate when she was a Sarkozy favourite. She has since fallen from grace, and when she left government she took a European parliament seat, considered a consolation prize.

She now wants to be a Paris MP. But Fillon wants the same Paris seat when he steps down, after next year's election. Both have their eye on the main prize: running for Paris mayor in 2014.

For months, Dati warned she would refuse to stand aside. Now she has stunned the political class with an open letter to Fillon in Le Monde, a scathing character assassination accusing him of the "lone ambition" of a disillusioned political elite, of doing politics in a way that "never favoured women" and stopping ethnic-minority candidates from progressing at elections. She said he was committing "a sad mistake" in trying to run in Paris.

She suggested he was destroying all Sarkozy had achieved in proving that a traditional, Catholic, rightwing area could vote for an ethnic-minority candidate such as her, from a poor housing estate in the provinces, the Muslim child of illiterate north African parents. She vowed to "resist" Fillon.

The letter provoked an angry response from several rightwing politicians within her party. One Paris MP, Bernard Debré wrote Dati a vicious open letter calling her a silly, ungrateful, arrogant "spoilt brat". He pointed to a poll on Sunday that showed Fillon winning 39% of the vote in the constituency, with Dati on 8%.

The junior minister Nadine Morano, who recently said Dati had been served a political career "on a golden platter", suggested she go back to her roots and run in rural Burgundy, where she grew up in a poor family of 11 children.

Some commentators wondered if Dati was being used as part of an internal battle between Fillon and the head of Sarkozy's UMP party.

But the row highlighted the fall from grace of the ethnically diverse women Sarkozy once promoted but later cast aside, who are now rebelling. The former young sports minister, Rama Yade, outspoken and hugely popular, has not only quit the government: she has left Sarkozy's party.

Meanwhile, the left is deliberately running more ethnically diverse candidates in the parliamentary elections next year, claiming Sarkozy's one-time "rainbow" cabinet of racially diverse women had turned out to be window dressing.